A use of nitrogen which is becoming increasingly more important is as a fluid for use in secondary oil or gas recovery techniques. In such techniques a fluid is pumped into the ground to facilitate the removal of oil or gas from the ground. Nitrogen is often the fluid employed because it is relatively abundant and because it does not support combustion. When nitrogen is employed in such enhanced oil or gas recovery techniques it is generally pumped into the ground at an elevated pressure which may be from 500 to 10,000 psia or more.
Often it is desirable to have available oxygen, either at ambient or elevated pressure, for use in a process proximate to that which uses elevated pressure nitrogen. For example, in one such situation it may be desirable to supply lower purity oxygen for combustion purposes to generate synthetic fuels and elevated pressure nitrogen for enhanced oil or gas recovery. Another such combined product application could be in metal refineries and metal-working operations which can utilize elevated pressure nitrogen for blanketing purposes and low purity oxygen for combustion; some high purity oxygen could also be used for metal working operations. Still another application could be in chemical processes where the nitrogen is used for blanketing and the oxygen is used as a chemical reactant. Although there are known processes to produce nitrogen and oxygen, it would be desirable to have a process which can produce large quantities of elevated pressure nitrogen and also produce some oxygen.
A known process to produce nitrogen and oxygen employs compressed feed air to reboil the lower pressure column bottoms. Such a process is generally termed an "air boiling" or a "split column" process. A split column process may be advantageous over a double column process because it can have improved separation efficiency and can have lower equipment costs. For this reason, it would be desirable to have a split column process which can produce large quantities of elevated pressure nitrogen and it would also be desirable to have a split column process which can produce large quantities of elevated pressure nitrogen and also some oxygen.
It is therefore an object of this invention to provide a split column air separation process which will produce large quantities of nitrogen at elevated pressure and at a high separation efficiency.
It is a further object of this invention to provide a split column air separation process which will produce large quantities of nitrogen at elevated pressure and at a high separation efficiency while also producing some oxygen.